1. Field of the Invention
The present invention relates generally to a method and device for detecting the charge level in an air conditioning system, and more particularly, to a method and device for detecting the charge level in an automobile air conditioning system.
2. Discussion
Automotive air conditioning systems include a compressor, a condenser, an expansion device, and an evaporator connected by conduits to form a closed system. A mixture of refrigerant and oil, referred to as refrigerant charge, is circulated through the air conditioning system to produce cool air. The compressor receives the necessary lubrication from the oil in the refrigerant charge to circulate the refrigerant charge to the condenser, expansion device, and the evaporator. If the compressor is forced to function when the refrigerant charge is low, it can be damaged. The low refrigerant charge will cause increased compressor operating temperatures which would cause a reduced cycle system and an increase of compressor on time. Further, the low refrigerant charge can lower the mass flow rate decreasing the availability of the lubrication oil for the compressor and also causes the compressor to run hot. Therefore, the compressor will not receive enough lubrication oil to operate the system properly and will become damaged if it continues to operate.
There are a number of systems known to detect the charge in air conditioning systems. The refrigerant charge in a system has been measured by monitoring the pressure and temperature outside the compressor. If the system produces a high temperature and a low pressure outside the compressor, a low charge signal is indicated. Further, the refrigerant charge in a system has been measured by measuring the temperature and pressure after each process of the system. The measured values are compared to predetermined values to calculate the refrigerant charge. However, these methods can be inaccurate when determining the refrigerant charge level because the refrigerant charge is also effected by the compressor speed, air flow through the evaporator and the condenser. Consequently, if the inadequate charge level is not corrected immediately, the compressor will become damaged and can break down.
Therefore, it is desirable to improve the accuracy of detecting the refrigerant charge in an air conditioning system. Further, it is desirable to increase the durability of the compressor in the air conditioning system.